Conventionally, spiral heat exchangers are manufactured by means of a winding operation. The two flat sheets are welded together at a respective end, wherein the welded joint will be comprised in a center portion of the sheets. The two sheets are wound around one another to form the spiral element of the sheets so as to delimit two separate passages or flow channels. Distance members, having a height corresponding to the width of the flow channels, are attached to the sheets.
Two inlet/outlet channels are formed in the center of the spiral element. The two channels are separated from each other by the center portion of the sheets. A shell is welded onto the outer periphery of the spiral element. The side ends of the spiral element are processed, wherein the spiral flow channels may be laterally closed at the two side ends in various ways. Typically, a cover is attached to each of the ends. The covers may include connection pipes extending into the center and communicating with a respective one of the two flow channels. At the radial outer ends of the spiral flow channels a respective header is welded to the shell or the spiral element forming an outlet/inlet member to the respective flow channel.
To improve the heat transfer between the fluids in the spiral heat exchanger, which heat transfer surface traditionally is formed by a wound flat plate, attempts have been made to use corrugated sheets similar to those used in plate heat exchangers.
In the European patent document EP-B1-1 295 077 a spiral exchanger is shown, consisting of two overlapping fluid circuits, a first circuit formed by the space included between two spaced sheets wound on themselves and a circuit formed by the space included between the successive turns of said winding. The sheets comprise, on their opposite surfaces, spacing elements, said spacing elements being arranged along the longitudinal axis of the sheets, so that, once the sheets are wound, the spacing elements of a sheet are urged to be pressed on the corresponding spacing elements of the other sheet, the end surface of at least one of the two pressed spacing elements is globally planar. The spacing elements and the corrugations are formed from the sheet.
In the Chinese patent application CN1667341 a spiral corrugated plate heat exchanger is disclosed having sheets provided with a corrugated surface. The height of the peak valley of the corrugated surface determines the width of two fluid channels.
In the Japanese patent document JP-A-6273081 a spiral heat exchanger is disclosed, the spiral heat exchanger is formed by winding a heat transfer plate, which comprises stud pins as spacers at a one-way channel, and disturbance bars at the other channel. The bars are intermittently arranged in a zigzag manner, and mounted at an angle to extend in an advancing direction of fluid. Accordingly, since the intermittent bars are arranged in the zigzag manner, the fluid is dispersed and mixed to improve heat transfer performance.
In the Russian patent document SU898255 a heat exchanger is disclosed having corrugated sheets twisted in spirals and having spacing pins arranged between the sheets to absorb force loads.
None of the above suggested attempts to improve the heat transfer of a spiral heat exchanger fully succeeds in providing a good solution, since they are either too complicated in their construction or merely tries to copy features of plate heat exchangers into the spiral heat exchangers without adapting them to the characteristics of the spiral heat exchanger.